Problem: Suppose the area of a circle is ${25\pi}$. What is its circumference?
Explanation: ${K = 25\pi}$ ${c = 10\pi}$ First, find the radius: $K = \pi r^2$ , so $r = \sqrt{K / \pi} = \sqrt{{25\pi} / \pi} = {5}$ Now find the circumference: $c = 2\pi r = 2\pi \cdot {5} = {10\pi}$.